On Wednesday I had an opportunity to speak with Chris Cassidy, a former Navy SEAL and astronaut who just returned from a 166-day stint aboard the International Space Station on Sept. 11.

Cassidy was the lead spacewalker during the dramatic July 16 spacewalk in which the helmet of fellow spacewalker Luca Parmitano dangerously filled with water. In part due to Cassidy’s cool-headed actions and leadership, Parmitano made it safely back inside the station.

Anyway, Cassidy has performed six spacewalks, so I couldn’t resist asking him about Gravity. He’d seen the trailer. Is that something he’s ever thought of?

“That’s really something we do think about. Especially during the first hours of the first spacewalk, you’re thinking about not letting go. I definitely never have more than one hand off of that space station. You don’t want to be the astronaut who has to rely on a safety tether.”